Marmaduke destroyed his owner-family's mailbox (and probably a number of other things) during his afternoon walk with his owner-man. Owner-Man makes light of the mailbox situation to his wife, yet another example of how the bulk of their communication is a numb, disconnected and empty series of weak jokes and ironic understatements deployed in order to distance themselves from the horror and futility of spending their lives as the prisoner-slaves of their powerful, self-serving ogre of a dog.